Accurate Intramolecular Forces Within Gaussian Orbital Local-Density Framework: Progress Towards Real Dynamics

Abstract

With the results of a multitude of numerical tests of the Hohenberg-Kohn-Sham local spin density (LSD) approximation (Hohenberg et al., 1964, Kohn et al., 1965) in hand, there is a growing consensus amongst researchers concerning the long term viability of the LSD approximation over other ab initio techniques for applications to large molecules. Coupled with the ever increasing numerical data base of results is an enhanced formal understanding of the relative attributes and shortcomings of the existing approximations to the universal functional. The consensus that has emerged is that the existing LSD approximation is expected to give very accurate information about ground state molecular geometries (eg bond lengths and angles), molecular vibrational phenomena, and qualitatively correct energetics. While improvements of LSD based molecular energetics is currently a field of active research, there is confidence within the chemical and physical communities that slight improvements to the approximations will lead to quantitatively correct energetics as well. For this reason, many researchers have turned toward merging classical molecular dynamics and quantum mechanical electronic structure techniques by incorporating atomic forces, calculated within the LSD framework, into dynamical or quasidynamical algorithms. The primary focus of this paper will be on some of our recent work toward this goal.